Earth-boring bits are commonly used for drilling bore holes, or wells, in subterranean formations. Conventional rotary earth-boring bits are typically classified into two types: roller cone bits and fixed-cutter bits (often referred to as a “drag” bit). A conventional roller cone bit has one or more generally conic roller cones rotatably mounted on the bit body. The roller cones have cutting teeth and/or inserts extending therefrom and rotation of the bit body rotates the cones so that the cutting teeth and/or inserts crush and gouge the formation. Conventional drag bits typically have no moving parts and include cutting elements which scrape across and shear away the underlying formation material.
The cutting structures of both of these types of bits are cooled and cleaned by drilling fluid provided to the bit surface during the normal drilling operation. The drilling fluid is conventionally pumped down a drill string having the bit at the end thereof, and out through a plurality of apertures in the bit face. The drilling fluid flows out the plurality of openings to the bottom of the borehole and carries the removed formation material, entrained in the drilling fluid, away from the surface of the formation being drilled and back up the hole on the outside of the drill string.
In some applications, nozzles are inserted and secured into the apertures to direct the drilling fluid and/or to provide high velocity jets of drilling fluid. Typically, tungsten carbide nozzles having specific flow diameters are employed. The ability to replace these nozzles in a drill bit is desirable in order to enable altering the hydraulic characteristics for differing service conditions.
Conventional roller cone bits may use a cylindrical nozzle insert with a constant outer diameter, as shown in FIG. 1. For securing the nozzle insert 100, the aperture 110 in the bit body may have a retention ring groove 120 machined near the bit face 130. The nozzle insert 100 is placed in the aperture 110 and secured with a conventional circular metal spring retention ring 140. One problem with exposing the retention ring 140, however, is the potential for erosion of the retention ring 140 by impingement of the high velocity drilling fluid. Although there is less potential for erosion caused by so-called “splash-back” of the drilling fluid off the adjacent borehole surface in a conventional rotary cone bit where the exit position of the nozzle insert 100 is relatively distant from the borehole surface, the retention ring 140 can still be subject to the erosive forces of the high velocity drilling fluid and entrained formation particulates.
A conventional fixed-cutter, or drag, bit on the other hand, typically cannot employ an exposed conventional retaining ring as a nozzle insert retention method because the exit position of the nozzle insert is relatively close to the borehole surface. An exposed retaining ring would thus be exposed to severe splash-back of the high velocity drilling fluid, eroding the retaining ring and eventually causing failure thereof and loss of the nozzle insert. Therefore, as illustrated in FIG. 2, a nozzle insert 200 for a fixed-cutter bit typically has a thread 210 formed into the insert material. A complementary thread 220 is also formed in the aperture 230 when the bit body is formed, thus allowing the nozzle insert 200 to be screwed into the aperture 230. Although the threaded retention system shown in FIG. 2 is generally effective, the cost of forming the complementary thread pairs is relatively expensive due to the difficulty to machine material of the inserts, generally tungsten carbide.
There is a continuing need in the art for better and more cost-efficient techniques for securing insertable devices, such as nozzle inserts, within an aperture in a receiving device, such as an earth-boring drill tool or other downhole tool, which are adapted for substantially protecting the retention mechanism from an external environment, and in which the retention mechanism is relatively easily engaged and disengaged.